Site of Ammonia to Uric Acid Conversion in Birds

The site of conversion of ammonia (NH₃) into uric acid in birds is:

Correct Answer: Both liver and kidney

In birds, the conversion of ammonia (NH₃) into uric acid occurs in both the liver and the kidney.

Nitrogen Excretion: Mammals vs. Birds

• Mammals: NH₃ is converted to urea in the liver (via urea cycle) → excreted in urine. Principal nitrogenous component of mammalian urine = Urea
• Birds: NH₃ is converted to uric acid in both the liver AND kidney → excreted as white, semi-solid paste. Principal nitrogenous component of avian urine = Uric acid

Why Birds Excrete Uric Acid Instead of Urea

• Uric acid is almost insoluble in water — can be excreted as a paste with minimal water loss
• This is an adaptation for water conservation, especially in eggs (embryos cannot dilute ammonia in a closed shell — they produce uric acid which is stored safely)
• Uric acid is also less toxic than ammonia

Additional Avian Renal Facts

• Urinary bladder is absent in birds (fowl)
• Major post-renal modification of ureteral urine in birds occurs at the colon
• Yellow colour of urine (mammals) = urobilin